1. Field of the Invention
The present invention relates to a method for obtaining a good-quality semiconductor crystal independent of a starting substrate by growing a semiconductor crystal of a Group III nitride compound semiconductor on the starting substrate.
The invention can be applied to production of a crystal growth substrate for various kinds of semiconductor elements such as an LED.
2. Description of the Related Art
As the related art for obtaining a semiconductor crystal independent of a starting substrate by growing a semiconductor crystal of a Group III nitride compound semiconductor on the starting substrate, there are generally known: a method using wet etching described in Unexamined Japanese Patent Publication No. Hei-7-202265: “Method for Producing Group III Nitride Semiconductor”; a method in which a sapphire substrate is removed by laser irradiation, polishing or the like after a thick GaN film (target semiconductor crystal) is grown on the sapphire substrate by an HVPE method or the like; and so on.
In the related art, there is however a problem that a large number of dislocations and cracks occur in the target single crystal because stress caused by the difference in thermal expansion coefficient or lattice constant between the starting substrate (e.g., sapphire) and the Group III nitride compound semiconductor is applied to the target single crystal (e.g., GaN) at the time of cooling or the like after the completion of the crystal growing step.
When, for example, the related art is used, the problem is as follows. When a crystal of a nitride semiconductor such as gallium nitride (GaN) is grown on a starting substrate made of sapphire, silicon (Si) or the like and then cooled to the ordinary temperature, a large number of dislocations and cracks occur in the nitride semiconductor layer because of stress caused by the difference in thermal expansion coefficient or lattice constant.
If a large number of dislocations and cracks occur in the growth layer (nitride semiconductor layer) as described above, lattice defects or a large number of dislocations, deformations, cracks, etc., occur in a device when the device is formed on the growth layer. This causes deterioration of device characteristic. Moreover, when the starting substrate is removed while only the growth layer is left as an independent substrate (crystal), it is impossible to produce a large-area crystal because of the function of the dislocations, cracks, etc. In addition, when a thick film is grown, cracks occur in the target single crystal even during the growth. There arises very easily the problem that peeling into small pieces occurs partially.